AR 10037990, Operating And Service Manual, Page: 30 / 54

Model 250T6G18
10 Rev A
3.2.5 RF Connections
The RF output connector is type WRD-650.
CAUTION:
Never operate the TWTA without a matched output load rated for at least
350 watts, continuous. The TWTA is not provided with an output
isolator. Full reflected power may irreparably damage the TWT. Even
with no drive, "looping" oscillation can result in RF output high enough
to damage the tube if it is operated without a load. The VSWR detection
and foldback circuit is provided to protect the tube from progressive
failure or mismatch of the output load; it should not be relied on for
protection from the absence of a load.
If an external isolator is installed at the output of the TWTA, either the isolator should have a load capable of
dissipating the full output of the TWTA or the isolator load should be provided with a temperature sensing switch.
The temperature switch should be normally closed, self-resetting, and with a temperature rating such that there is
no possibility of damaging the load by overheating before the switch opens. The TWTA may be interlocked with
the switch by connecting it between pins 3 and 4 of the external interlock connector (J3). If no external isolator is
used, install a jumper between pins 3 and 4. See Section 3.2.6, External Interlock Connector, below.
3.2.6 Waveguide Installation
The following procedure is to assure waveguide is inspected for defects and installed correctly.
1. Visually inspect outside of waveguide to confirm part is not bent. If part is bent, do not proceed.
2. Using a flashlight, visually inspect inside of waveguide from both ends. Look for any debris. If there is debris
in the part, do not proceed.
3. Visually inspect ends of waveguide for flatness. Both ends should be flat and without nicks. If it is not, do not
proceed.
4. If gasket is required, install it at this time.
NOTE: Some gaskets have a flat side and a rounded side. In these cases, install the gasket flat side first
(into groove).
5.
To ensure the gasket stays in place, apply a light film of DOW CORNING HIGH VACUUM SILICONE
GREASE to the flat side of the gasket prior to installing in groove.